#include <stdio.h>

int sum(int m, int n);
int a;
int main()
{    
    int m, n, i;
    scanf("%d %d", &m, &n);
    //printf("sum = %d\n", sum(m, n));
    int sum = 0;
    for(i = m;i <= n; i++) {
       sum = sum + i; 
    }
    printf("%d", sum);
    return 0;
}